The present invention relates to a wall element for an underground gallery, particularly for a rigid or peripherally yieldable arcuate underground gallery. More particularly, the present invention relates to a wall element which is formed as a W-shaped member with bent away flanges, is symmetrical relative to a y-axis, formed so that its axis of gravity coincides with its x-axis and lies at least approximately in the center of the height, and has, in condition of considerably greater width than height such thicknesses of its base portions, flange portions and connecting web portions that, in relation to used weight per meter, it has a maximum possible moment of resistance relative to the x-axis and also a maximum possible bending load capacity in a plastic deformation region.
Wall elements of the above mentioned general type for arcuate, rigid or peripherally yieldable galleries are known in the art, for example from French Pat. Nos. 1,017,752, 802,413, or 967,283. They are also formed as pure roof bars or covers for galleries, as disclosed in the British Pat. No. 23,736 or the publication "Stahl e,uml/u/ berall", Vol. 4, 1935, page 38, Picture 63.
The wall elements of this type could not be used opposite to the double-webbed groove-shaped members, at least for the utilization in rigid or peripherally yieldable arcuate galleries. This is connected, first of all, with the fact that the conception of a W-shaped member serving as a wall of a gallery starts from an assumption of assembling two known double-webbed groove-shaped members. The W-shaped member produced in accordance with this conception has a doubled weight per meter and also a substantially doubled moment of resistance relative to the x-axis, as compared with the individual double-webbed groove-shaped members. Its utilization with rigid or peripherally yieldable arcuate galleries was considered as effective only in the event that there is a possibility to increase the distance of the arc in the longitudinal direction of the gallery, or practically to double the same. This assumption, however, fails when the groove-shaped member with high weight per meter is required, namely in galleries, particularly face roads which are continuously subjected to particularly high rock pressure applied from the mine face.
In practice, it is preferred to put the respective known two-webbed groove-shaped profiles in connection with an increasingly high weight per meter to a respectively high moment of resistance, particularly relative to the x-axis, and to introduce wall arcs assembled therefrom in short distances from one another. For these reasons, the known W-shaped members are practically replaced and, retroactively speaking, belong to paper art.
The present invention deals with a W-shaped member which was known for a long time for arcuate galleries with a completely new point of sight so that it is principally advantageous than the conventional two-webbed groove-shaped member which has increasing disadvantages in the fact that, when it is installed with its flanges or base portions toward rock, it provides for bending load capacities considerably deviating from one another. The difference in the bending load capacity can amount to 100% (Streckenausbau in Stahl, by Dr. Spruth Verlag, Gluckauf GmbH, Essen, Issue 1955, page 106, paragraph 2 in connection with Picture 75 on page 110).
All attempts to eliminate or reduce these disadvantages of the double-webbed groove-shaped members on the way to pure optimization of the profile have failed. As a result of this, the disadvantages are accepted and a compromise is selected, to arrange the double-webbed groove-shaped members with their flanges toward the rock. In this case considerably smaller bending load capacity (working capacity) is used in the region of the roof, which is accompanied by the advantage of considerably higher bending load capacity in the region of both lateral thrust sides.
Considerations which take place here include that bending stresses which act from outside in the roof region of a wall curve as a resultant of the depth pressure act in predominant cases in a radius increasing manner, whereas in the region of both lateral legs at thrust sides they act in a radius reducing manner. The radius increasing load in the arc regions, i.e., first of all in the roof region, are considered to be sufficient when the flanges of the shaped member form a pressure zone, inasmuch as in the region of both thrust sides considerably high bending load capacity of the lateral legs can be exhausted relative to the opposite bending moment, when not the flanges but instead the base portions form the pressure zone.
Taking into consideration the considerably different bending load capacities depending upon whether the flanges or the base portions lie in the pressure zone, it is naturally desirable to arrange the double-webbed groove-shaped members in the roof region and in both thrust regions opposite to one another. This, however, is possible only in the event of multi-partite rigid curved walls, but not in a peripherally yieldable curved wall in which the grooved segments must be arranged in the same direction in one another to function properly.
Even without these disadvantages, such a solution encounters in practice considerable difficulties, inasmuch as it is impossible to predict at which location of the curved wall the region of the positive bending moment transit into the region of negative bending moment, since the location of the bending moment-reversing point depends on the outer loading conditions under the action of the rock pressure, and the bending stress is applied as a rule not centrally but eccentrically wherein the value of the eccentricity cannot be determined in advance.